The present invention relates to a sealing material made of a soft substance, particularly for the production of gaskets that are to be subjected to high stresses, such as cylinder head gaskets, exhaust flange seals and the like for internal-combustion engines. The gasket comprises an asbestos-free, possibly metal reinforced, fiber sheet including fibers of synthetic or natural, organic and inorganic origin, with the fiber sheet possibly being impregnated with synthetic organic substances which, in their final state are plastically deformable or elastically cross-linked.
In practice, conventional cylinder head gaskets made of a soft substance for use in internal-combustion engines are usually made of possibly metal reinforced asbestos fiber sheets. These may be impregnated, for example, as disclosed in DE-AS No. 2,304,558 and corresponding U.S. Pat. No. 4,201,804 to Stecher et al, with a substance which, in its final state, is plastically deformable or elastically cross-linked.
With respect to their physical and chemical characteristics, asbestos fibers are the ideal material for the production of fiber sheet plates for cylinder head gaskets. It is known that asbestos fibers are heat resistant and sufficiently soft and elastically deformable. Moreover, asbestos fibers can be processed into fiber sheet materials in processes similar to those used in the production of paper so as to exhibit deformability, strength, porosity and stability suitable for use in cylinder head gaskets. On the other hand, asbestos fibers and asbestos dust are known to be a great health hazard so that it is to be expected that in the future the use of asbestos will be restricted considerably and most likely even entirely forbidden for the manufacture of certain products.
It has therefore been attempted to produce soft material gaskets of fiber sheets on the basis of inorganic or organic natural or synthetic fibers. Since the prior art fibers alone do not simultaneously possess all of the ideal physical characteristics of asbestos, it has been attempted, for example as disclosed in German Pat. No. 2,914,173, to produce fiber sheet materials for cylinder head gaskets by combining mixtures of two different types of fibers, namely natural organic fibers on the one hand and synthetic organic or inorganic fibers on the other hand. For example, according to DE-OS No. 2,730,588, the fiber panels intended, in particular, for the production of floor coverings, sealing plates or wall coverings are made of 40 to 60% vegetable fiber, 10 to 30% latex binders and 10 to 50% fine-grained mineral fillers.
However, cylinder head gaskets made of these combinations of materials for internal-combustion engines are not fully satisfactory and, with respect to the required, quite specific technolgoical properties, such gaskets are inferior to the previously employed cylinder head gaskets made of asbestos fiber sheets. For example, the plate material according to DE-OS No. 2,730,588 in particular did not exhibit the great strength and heat resistance required for cylinder head gaskets. Further, the plate material according to DE-OS No. 2,730,588, as well as the material according to DE-PS No. 2,914,173, could not be compressed sufficiently to the required density or porosity, respectively, so that subsequently the material could no be impregnated sufficiently.